1. Field of the Invention
The present invention relates to a through hole formation state detecting device which determines an aligning state of apertures each provided in a respective one of a plurality of moving members, thereby determining whether a though hole is formed through which light can pass. The present invention also relates to an electronic timepiece which detects an aligning state of apertures each provided in a respective one of a plurality of gears or wheels which drive hands of an analog display, thereby detecting the position of the hands.
2. Description of the Related Art
Analog display timepieces are known which receive a standard time and frequency signal to automatically set a time to time codes of the frequency signal. Other electronic timepieces are also known in which an operation button is operated to electrically drive and rotate the hands, thereby setting various functions, for example, including setting an alarm time. Such functions are achieved by rotating the hands after the controller recognizes the position of the hands.
When electronic timepieces having an analog display are put in a strong magnetic field or shocked greatly, the hands can become offset from their positions which the controller has recognized. Unless the hands are set to their positions which the controller has recognized, the time indicated by the hands is left offset from a correct time. In order to avoid such undesirable situation, recent electronic timepieces have an internal hand position detector which confirms at predetermined intervals of time whether the hands are offset from the correct time. Some electronic timepieces have been developed which have the function of automatically correcting the hand positions when detecting the hand offsets.
A hand position detecting mechanism is known, which includes a photo-interrupter which detects alignment of a plurality of apertures each provided in a respective one of gears moving along with the corresponding hands, for example, as disclosed in Japanese Published Unexamined Patent Application 2000-162336.
Further, prior art techniques related to the present invention are, for example as follows. Japanese Published Unexamined Patent Application 2007-40863 discloses a wristwatch which includes a photosensor of a photo-interrupter which detects the position of a hand, provided on the side of a dial where external light is difficult to enter the photosensor and a light emitting element provided on the side of a back plate of the timepiece in order to prevent wrong detection due to the external light entering the photosensor. Japanese Published Unexamined Patent Application 2002-42262 discloses a technique for negating testing of a fire alarm, which detects a fire with a photosensor and reports it, when strong external light enters the fire alarm during the testing. Japanese Published Unexamined Patent Application Hei 05-199178 discloses a remote controller which includes a photodetection unit which senses external light with two sensors, and which weights the signals differently from the two sensors to reduce the influence of external light, thereby receiving a remote control signal.
In the device disclosed in the Application 2007-40863, when external light enters the photodetection element of the photo-interrupter, the device may wrongly detect an aligning state of the apertures in the gears.
Generally, external light often enters the timepiece through a hand aperture provided at the center of the dial. When the dial is formed of a liquid crystal panel or a solar panel as the timepieces become multifunctional, the dimensional accuracy of the hand aperture in the dial is somewhat deteriorated, thereby somewhat increasing an amount of external light entering the timepiece.
Since light is randomly reflected within the timepiece by various parts included in the timepiece, it is difficult to prevent external light which has entered the timepiece from entering the photodetection element even when the arrangement of the photointerrupter is changed.
Further, in the photo-interrupter, it is usually determined that there is a through aperture in moving members between the light emission element and the light detection element when the light detection element receives light having a strength more than a predetermined threshold from the light emission element through the through apertures in the moving members. If a circuit configuration is used which determines the presence of a through aperture using a digital control circuit such as, for example, a microcomputer, it usually performs AD conversion on received light of the photo-interrupter, and compares a resulting value with a threshold, thereby determining whether there is a through hole formed. Especially, if the threshold is settable as a variable digital value, usually, the light received by the photodetection element is subjected to AD conversion, and then captured.
When a general successive comparison type AD converter is used, the AD conversion requires a time of a plurality of clocks depending on the resolution of AD converter. Thus, if it is required to try to find the presence of a through hole successively many times, it would take much time until the through hole is found. Such problem becomes remarkable when the hands are rotated at high speeds to locate a predetermined arrangement of the gears in the hand position correcting process, for example, for an analog display timepiece.
The light emission element is required to continue to emit light in the AD conversion. Thus, when the time required for the AD conversion increases, the emission time of the light emission element and its consumption power would increase. Such problem becomes remarkable, for example, when a wristwatch which is driven by a battery employs a method of determining whether a through hole is formed, by performing the AD conversion many times.
The problem of a deterioration in the detection accuracy of the through hole due to external light, and the problem of consumption of the time and power required for determination of the through aperture to be made many times in the AD conversion of the received light occur not only to the analog display timepieces but also to various other devices in which the photo-interrupter detects a hole formed based on aligning apertures in the moving members.